The invention concerns a tooth set for a hydraulic machine, particularly a steering unit, with a toothed ring, having teeth, which are formed by means of inserts arranged in a housing, and a gear wheel arranged inside the toothed ring.
Such a machine is known from U.S. Pat. No. 3,289,602.
In the following, the invention is described on the basis of so-called xe2x80x9corbitxe2x80x9d machines, in which the gear wheel has one tooth less than the toothed ring and the gear wheel orbits and rotates in the toothed ring. This movement causes the teeth of the gear wheel and the teeth of the toothed ring to form limitation spots for individual pressure pockets, each pressure pocket being alternatingly exposed to pressure and relieved during motor operation. During motor operation the situation is directly reversed: Pressure pockets with a volume, which is reduced at a further movement of the gear wheel, are connected with a pressure connection, whereas pressure pockets, whose volume increases at the further movement, are connected with a suction connection. The efficiency of such machines is determined by, among other things, the inner tightness, that is, by the reliability, with which the individual pressure chambers are sealed against each other at the contact spots of the teeth of gear wheel and toothed ring. The same problems also apply for other tooth sets for hydraulic machines, in which a sealing between pressure chambers is also required, for example gerotor machines.
The tightness can be improved in that very narrow fits are provided between the toothed ring and the gear wheel. However, this causes that the frictional losses get very high, and that a substantial wear occurs. Additionally, the production of such tooth sets is relatively expensive.
Thus, it is proposed in U.S. Pat. No. 3,289,602, mentioned in the introduction, to form the teeth of the toothed ring from small tubes, which are supported in corresponding bores in the housing. In this connection, the tubes, or at least their surfaces, can be made of a very hard material, while the housing can be made of a softer material, which is consequently cheaper to work. In an alternative embodiment the tubes are replaced by cross-sectionally square bars, which are rounded in the area of the teeth and supported in the housing with a play, so that their angle position in relation to the gear wheel changes in dependence of the actually ruling forces. The same adjustment opportunity is also available for the tubes.
The invention is based on the task of simplifying the production of a tooth set.
With a tooth set as mentioned in the introduction, this task is solved in that at least at its ends each insert has a plate-like shape and that the ends are fixed in the housing in corresponding slots.
This embodiment has the advantage that the inserts can be substantially simplified, and still be retained reliably in the housing. The material of the inserts and the material of the housing can be chosen independently of each other, the material of the inserts being chosen with a view to wear resistance and a good cooperation with the teeth of the gear wheel. The housing only has to be stable enough to stand the ruling pressures. A resistance towards the wear of the gear wheel, however, is no longer required. As now, the efforts can be concentrated on inserts, on which the xe2x80x9cbearing surfacexe2x80x9d, that is, the area along which the teeth of the gear wheel are rubbing, is clearly defined and thus limited, the cost for the material will be kept low. The plate-like shape of the ends gives surface sections, through which the inserts are retained radially and in the circumferential direction, without requiring an expensive working of the housing.
Preferably, the insert is made of a bent plate. Such a plate is easily produced, and in this connection the term xe2x80x9cbentxe2x80x9d refers to the final state, that is, the curve shape can also be made in other ways than by means of the production process of bending. Through a bending process, however, the insert can be provided with a certain pretension, so that a certain internal tension helps retaining it in the slots in the housing.
Preferably, the insert is made of spring steel. Spring steel is a relatively hard material, so that the xe2x80x9cteethxe2x80x9d or the wearing surfaces of the teeth consist of a correspondingly resistant material. Spring steel is a relatively inexpensive material. The surface of spring steel needs practically no further working, like for example a hardening, which simplifies the production further.
Advantageously, the slots are directed so that they form a predetermined angle to the radial direction. Thus, the slots can be inclined somewhat in the tangential direction, so that the insertion of the plate-like ends is facilitated. For example, the slots can have a direction, which corresponds to the tangent of a circularly bent tooth in the spot, where the insert projects into the housing.
Preferably, at each insert the housing has a radially inward projecting boss, which fills a space surrounded by the bent plate. Thus, the housing supports the tooth, that is, the bent plate. Or, to put it simply, the tooth is still formed by the housing, the bearing surface being covered by the insert. Thus, the toothed ring can be produced very accurately, without requiring the use of expensive materials. However, a very good wear resistance is still obtained.
In an alternative embodiment a gap may exist between the bent plate and the housing. No longer being supported by the housing, the bent plate is therefore a little flexible. This gives each tooth a small flexibility or elasticity, so that a pairing grinding, which is used for almost all tooth sets today, can be avoided. The flexibility of such a tooth is extremely small. At the highest, it is in the xcexcm-area. However, it is sufficient to permit a substantial reduction of the accuracy of the fit between gear wheel and toothed ring.
Preferably, the housing-side limiting wall of the gap is formed by a circumferential cylinder surface, whose diameter corresponds to the inner diameter of the housing. Additionally to the flexibility or elasticity of the tooth, this gives an additional production advantage. The housing can be made as a simple cylinder ring, which is very easily produced, for example by turning. The slots for adopting the insert merely have to be made in the inside of this cylinder ring.
Preferably, the gap is filled with a compressible material. Such a material can, for example, be rubber or another elastomer material. Thus, on the one hand, the resilience of the tooth is maintained. On the other hand, however, the tooth is in some way supported from the inside. Additionally, this embodiment has the advantage that the insert can be prestressed from the inside, that is, from the housing, so that the insert is held firmly in the housing already then, when the gear wheel is not yet mounted.
In an alternative embodiment, the insert can be made of a profile, whose cross section is formed by the combination of a circle section and an oppositely bent rib, which projects sideward over the circle section. In this case, the plate-like embodiment of the insert can only be recognised at its ends in the circumferential direction. Otherwise, the insert is again a massive or, if desired, also a grooved body, at least a body, which obtains a three-dimensional extension not only through bending. However, also here the plate-like ends serve as holders for the teeth in the housing. Such inserts are also relatively easy to produce. For example, such inserts can be cut off from a profile. The inserts can be made of steel. Here, an additional advantage of these and the abovementioned inserts appears. The simple change of the length, which must be made simultaneously with a change of the axial length of housing and gear wheel, the output of the tooth set can be changed.
In this connection, it is preferred that the surface of the circle section is hardened. The other parts of the insert can remain unhardened. This embodiment firstly simplifies the production and secondly improves the operating behaviour.
Preferably, the inserts project axially over the front side on at least one front side, and the front side is covered by a plate, which has openings corresponding to the inserts. Thus, the front side sealing between the teeth of the toothed ring is displaced from the contact surface between the plate and the toothed ring into the inside of the plate. This gives substantial advantages. Thus, it is no longer necessary for the inserts to be plane parallel with the front side of the housing after mounting. Accordingly, a working with this purpose can be avoided. In the area of the teeth of the toothed ring, the tooth set is still xe2x80x9ctightxe2x80x9d, when, for example, the corresponding front side of the insert forms a small angle with the surface, or the insert has a certain roughness on the surface. Accordingly, the inserts can simply be cut off from a straight profile, for example by means of sawing. Thus, the inserts are already usable. A sealing is much more easily procured with an inserted part than with a merely bearing part.
In this connection it is preferred that the depth of the openings is larger than the projecting of the inserts. Thus, also the accuracy when cutting off and mounting the inserts can be reduced.
Preferably, in relation to the bearing surface, the housing is made of a soft material. A soft material is easier to work. It is usually cheaper. It only has to be sufficiently pressure resistant to adopt the pressures occurring during operation. There are no further requirements. Such a pressure resistance can, for example, be obtained in that on its radial outside the housing is wound with tightening straps, for example, fibre-reinforced tightening straps.
In a particularly preferred embodiment, it is provided that the surface of the teeth is smoothened in parallel to the movement direction of the gear wheel. Such an embodiment is only possible through the use of separate teeth in the toothed ring, as here the smoothing tool can be applied so that the smoothing tracks extend in the same direction, in which later also the gear wheel will pass the bearing surface of the individual teeth. In toothed rings, which are made in one piece, the smoothing tracks always extend perpendicularly to this direction, which gives noise during operation, which is to some extent disturbing.